The invention relates to a piston pump for a brake system of a vehicle.
The pump assembly of the invention is intended as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS (for anti-lock brake system), TCS (traction control system), ESP (electronic stability program) and EHB (electrohydraulic brake system) are used for such brake systems. In the brake system, the pump serves to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to pump brake fluid out of a supply container into a wheel brake cylinder or a plurality of wheel brake cylinders (TCS or ESP or EHB). In a brake system with wheel slip control (ABS or TCS) and/or a brake system serving as a steering aid (ESP) and/or an electrohydraulic brake system (EHB), the pump is needed. With the wheel slip control (ABS or TCS), locking of the wheels of the vehicle during a braking event involving a strong pressure on the brake pedal (ABS) and/or spinning of the driven wheels of the vehicle in the event of strong pressure on the gas pedal (TCS) can for instance be prevented. In a brake system serving as a steering aid (ESP), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal to prevent the vehicle from breaking out of the track desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB), in which the pump pumps the brake fluid into the wheel brake cylinder or wheel brake cylinders if an electric brake pedal sensor detects an actuation of the brake pedal, or in which the pump is used to fill a reservoir of the brake system.
Many such piston pumps are known. For instance, the piston pumps known from German Patent Disclosures DE 41 07 979 A1 and DE 44 07 978 A1 are set forth. The known piston pumps have a rod-like piston, which is axially displaceably guided in a bush. For driving the piston to execute a reciprocating stroke motion, an eccentric element is used that can be driven to rotate by an electric motor and that acts upon the piston on a face end protruding from the bush. The bush is inserted into a cylinder bore of a pump housing.
For assembling the known piston pumps, their pistons are introduced into the bush and are retained in the bush by the installation of a retention means. As the retention means, in the first reference cited, a rivet is inserted into a radial bore of the bush. The rivet protrudes on the inside, into an encompassing groove in the piston, which is wider by at least one piston stroke than a diameter of the rivet, and in this way secures the piston in the bush. In the second reference cited, a sleeve is press-fitted into one end of the bush. The piston of this piston pump tapers at an annular shoulder at which the sleeve press-fitted into the bush retains the piston in the bush. After that, the bush is screwed or press-fitted into the cylinder bore of the pump housing and caulked. Because the piston is secured in the bush for retention therein assembling the piston pump is made simpler, especially for piston pumps that have a piston restoring spring that presses the piston out of the bush.